1. Field of the Invention
The present invention relates to an ink unit for use in ink jet recording and an ink jet recording method and, more particularly, relates to a unit comprising an ink jet recording black ink and an ink jet recording chromatic color ink, and an ink jet recording method using this unit.
2. Description of the Related Art
So-called ink jet printers capable of recording images on paper, cloth, or film by discharging a liquid or molten solid ink through nozzles, slits, porous film, and the like have various advantages such as small size, low cost, low noise, and the like. In particular, a black monochrome printer is commercially available as a printer which can provide excellent printing quality on so-called ordinary paper such as report paper, copy paper, and the like. With the wide dissemination of this ink jet printer, various investigations have been undertaken with regard to the improvement of ink.
An ink for use in an ink jet printer has been studied taking into consideration the following five points:
(1) On paper, an uneven image with high resolution, high optical density, no bleeding, and no fogging can be obtained; PA0 (2) The tip of a nozzle is not clogged with dried ink, allowing the ink to provide excellent discharge responsiveness and discharge stability; PA0 (3) The ink dries quickly on sheet; PA0 (4) The resulting image has excellent fastness; and PA0 (5) The ink has excellent storage stability for a long period of time.
Various suggestions have conventionally been made regarding an ink for use in an ink jet printer to satisfy the above-mentioned requirements.
Aqueous dye inks have conventionally been used mainly as an ink jet ink. However, the aqueous dye ink has problems with regard to water resistance and lightfastness because the dye thereof is water-soluble so that the storage stability of the resultant image is not always satisfactory. On the other hand, inks which use a pigment improving water resistance and lightfastness as a coloring material are very useful, and many suggestions have been made regarding such color-pigment-containing inks, and have been practiced. For example, U.S. Pat. No. 5085698 suggests the use of an AB or BAB block copolymer as a dispersant, and U.S. Pat. No. 5172133 suggests the use of specific dyes, water-soluble resins, and solvents.
However, there are problems of poor color development property and marked unevenness on ordinary paper in printing, even though the color-pigment-containing ink has high waterfastness. Further, since the pigment particle components do not permeate but remain on the surface of ordinary paper, there is a problem regarding rub resistance due to rub on the surface. Further, the color-pigment-containing ink dries relatively slowly. Therefore, since the color ink comes in contact with other color ink which exists adjacent to it in a liquid state during drying, the bleeding thereof becomes a problem. In particular, when a full-color-pigment-containing ink is used, a poor color reproduction of shades and unevenness caused on ordinary paper are serious problems.